1. Field of the Invention
This invention relates to couplings used to join sections of pipe together into a continuous pipeline.
2. Description of Related Art
The conventional way to assemble pipelines is to weld individual pieces of pipe together For large diameter pipes, however, welding is a slow process. One way to avoid the high cost of welding is to use a sleeve-type coupling to fit over the two ends of the two pipes being joined.
Several sleeve-type couplings have been developed. Representative is U.S. Pat. No. 4,328,983 issued to Jack E. Gibson. The coupling consists of a sleeve having an internal diameter slightly smaller than the external diameter of the pipe sections to be joined. Forcing one end of a pipe section into each end of the coupling sleeve effects a press fit, sealed connection between each pipe section and the coupling.
Installation of couplings on pipe sections can be accomplished with a machine disclosed in U.S. Pat. No. 4,328,608 also issued to Jack E. Gibson. This machine grabs the outside of the pipe, grabs the end of the coupling, then forces the pipe into the inside of the coupling using two hydraulic cylinders which generate a force of approximately 120,000 lbs. Once the coupling is installed onto one end of a pipe, a second pipe can be installed, completing the joint. A major problem with this machine is that the hydraulic rams used to exert the forces necessary to accomplish the press fit must be mounted on a massive base which, in turn, can withstand the forces without becoming deformed. Consequently, this machine can only be used where there is ample, unobstructed space for its operation. Often it is used to construct underground oil transmission pipelines. The pipeline is assembled on the surface and then lowered into a trench. There normally is plenty of space around the trench, so the large size of the installation equipment is not a problem.
There are many instances where space is limited and the standard joining press cannot be used. One example is pipe containing high voltage electric transmission cables in an urban environment. Urban pipe-type installations are typically encumbered by frequent crossings of other utilities and by trench shoring, both of which prevent the lowering of a surface joined pipeline directly into the trench. Cramped quarters and the need to minimize trench size also prohibit placing the existing press into the trench for making the joint.
One solution to this problem is disclosed in U.S. Pat. No. 4,389,763 issued to Richard O. Marsh, Jr. The device used by Marsh has a slotted end plate which abuts the end of the pipe section opposite that to be inserted in the coupling. A hollow piston rod is attached to the end plate via a hydraulic cylinder and extends inside the pipe for the entire length of the pipe section. The hollow piston rod ends with a multi-fingered pawl mechanism which is used to grip a coupling previously installed on the other section of pipe. The coupling used with this device is a cylinder with annular grooves machined or cast in the ends of the cylinder. The ends of the pipe sections are press fit into the grooves on either end of the cylindrical sleeve. When the coupling is installed on one end of a pipe section, the resulting profile of the internal wall of the pipe-coupling combination contains an abrupt step formed by the end of the coupling sleeve. The pawl mechanism grips this step and the hydraulic cylinder puts the hollow piston rod in tension, thus drawing the end of the pipe section into the annular groove of the coupling.
Although this device reduces the size of the installation machinery, it has a number of significant drawbacks. The device is still quite large and unwieldy because the piston rod must be as long as the section of pipe being installed. The device cannot be used on pre-bent pipe because of the straight piston rod. Even if a flexible cable were substituted for the rigid piston rod, the device could not be used with bent pipe because the force is applied to the ends of the pipe and the eccentricity of the bent pipe would cause it to fold. And finally, the completed pipeline contains numerous steps along its interior which significantly increase pressure drop when the pipe is used to transport fluid or which significantly increase the chance of installation damage to insulation when the pipe contains electrical conductors.
It is an object of the invention to provide a small, compact pipe coupling apparatus which can be used in the confined spaces of a pipe trench.
Another object of the invention is to provide a pipe coupling apparatus which can be used to join pre-bent sections of pipe.
It is yet another object of the invention to provide a pipe coupling apparatus that results in a pipe joint without abrupt steps in the interior surface of the pipeline.
These and other objects are accomplished by the subject invention.